Adaptive equalizer training circuit, modem apparatus and communication apparatus

Abstract

A training circuit for training a tap coefficient of an adaptive equalizer that performs error calculations in a training process and updating of the tap coefficient in a time area and thereby makes the tap coefficient converge stably in a short time.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an adaptive equalizer applicable to a modem that carries out communication according to a frequency multiplexing system and a communication apparatus using the adaptive equalizer.[0003]2. Description of the Related Art[0004]As a technology for implementing high-speed data communication using a metallic cable, an ADSL (Asymmetric Digital Subscriber Line) is being developed. In an ADSL apparatus, transmission data is assigned to a plurality of frequencies, a few bits each, subjected to IFFT (inverse fast Fourier transform) and sent out to a transmission path. In the explanations hereafter, this system will be referred to as a “frequency multiplexing system”. The transmission data is divided into units of IFFT processing as one symbol, and a signal with a guard band to guard against interference between symbols added is sent out as one symbol. For example, in the case of G. Lite, which is o...

AI Technical Summary

Benefits of technology

[0018]It is an object of the present invention to provide an adaptive equalizer training circuit, modem apparatus and a communication apparatus using this adaptive equalizer training circuit capable of drastically reducing the amount of calculation during a training period and stably converging a tap coefficient without allowing calculation errors to get mixed by performing error calculations in the training process and updating of the tap coefficient in a time area.

[0021]Such an adaptive equalizer training circuit can directly perform error calculations and updating of the tap coefficient in the time area and can thereby adaptively equalize channel distortion of the transmission path using FIR filter w(t) and FIR filter b(t) bypassing FFT, and can thereby drastically reduce the amount of calculation during a training period and stably converge the tap coefficient without allowing calculation errors to get mixed.

[0023]According to such an adaptive equalizer training circuit, the target signal response updating section and tap coefficient updating section update the tap coefficient in the time area and the tap coefficient updating section even carries out an error calculation in the time area, and therefore it is possible to drastically reduce the amount of calculation during a training period and stably converge the tap coefficient without allowing calculation errors to get mixed.

[0025]In this way, an error calculation is performed after shifting the time-axis of the training signal received thereafter based on the maximum power area of the first calculated impulse response and adjusting the shifted time-axis to the beginning of the self-produced training signal, which requires only a first one calculation of impulse response, thus making it possible to drastically reduce the amount of calculation of impulse response in the training process.

[0027]Since the signal waveform of the maximum power area of the impulse response is given as an initial value of the tap coefficient in this way, the target signal fluctuates less, the tap coefficient generally converges more quickly and the amount of errors after convergence is also reduced.

Problems solved by technology

Thus, the adaptive equalizer above has a problem that the amount of calculation becomes enormous, and since calculations are made by reciprocating between the time area and frequency area, the adaptive equalizer above also has a problem that the filter factor includes errors, which reduces reliability.

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